The present invention relates in general to voltage regulators and, more particularly, to voltage regulators requiring very little quiescent current in a standby mode of operation.
Electronic devices such as Global System for Mobile Communications (GSM) cellular telephones and laptop computers generally require operational power in two separate modes of operation. A first mode of operation is provided such that the regulator is supplied enough quiescent current to allow sufficient noise immunity, Power Supply Rejection Ratio (PSRR) and dynamic performance, for example, requiring maximum quiescent current. A second mode of operation is characterized as a standby mode of operation, where the regulator supplies a coarsely regulated potential without the high performance specification requirements of the first mode. A fraction of the quiescent current, therefore, is needed in standby mode, to maintain only critical components required to detect a transition from standby mode into the fully operational mode at the desired time. The provisioning of two separate modes of operation, allows the electronic device to conserve energy during the standby mode of operation.
Prior art voltage regulators provide four main components. First, an error amplifier that generates an error voltage between the actual output voltage and the desired output voltage. Second, an internal voltage reference that generates a reference voltage, typically with a bandgap reference, which is used by the error amplifier to generate the error voltage. Third, a pass transistor, typically p-type, used to operate in linear mode, controlling the amount of current delivered to the load. Fourth, a buffer used to buffer the control input of the pass transistor from the output of the error amplifier.
Prior art voltage regulators employ error amplifiers designed to exhibit proper performance during nominal, or full function, operation. Full function operation of the prior art error amplifier requires enough quiescent current such that the error amplifier, for example, provides proper noise immunity while providing the specified dynamic performance. Typical quiescent current required by prior art regulators is approximately 30 micro-amps(uA) during full function operation. Prior art regulators, however, do not employ dual mode operation, whereby an idle or standby mode is detected with a subsequent reduction in power consumption during the idle or standby mode.
Hence, there is a need for a voltage regulator providing the ability to detect the standby operational mode and further implementing a reduction in power consumption while operating in the standby mode.